The present invention concerns a device for taking samples from a pipe loop carrying flowing liquid metal, particularly hot molten metal, consisting of a housing with inlets and outlets for the liquid metal, in which crucibles are arranged that can be filled with the liquid metal and taken out of the housing. The operational safety and efficiency of plants using such liquid metal, particularly of sodium-cooled nuclear power plants, depend heavily on the purity of the liquid metal, as impurities in the form of oxides form deposits which are hard to remove from equipment and which may, for instance, affect the functioning of valves adversely. Contamination by carbon can lead to carburization and corresponding embrittlement of the structural material used. It is therefore necessary to take samples of the metal at regular intervals, which samples can be analyzed for the presence of such impurities. Such an analysis can, of course, also serve for the determination of other substances, e.g., hydrogen. It is practical to fill the liquid-metal samples into crucibles, such as are commonly used in chemical laboratories. To ensure reliable analytical results, it is necessary to maintain a definite degree of filling of the crucibles and to prevent further impurities from penetrating into the samples while being taken. The samples should also be representative of the composition of the entire quantity of liquid metal, so that it is advisable to take it from a loop circuit, in which the liquid metal flows.
The analysis itself is usually performed in such a manner that the liquid itself, which is contained in the crucibles, e.g., sodium, is distilled off and the then remaining residue is examined chemically. Taking samples is made difficult to no small degree by the high temperatures prevailing in liquid-metal installations. If the liquid-metal is the coolant in a nuclear power plant, the liquid metal is more or less radioactive and requires a special design of the sampling apparatus as well as increased precautions in handling the samples.
Apparatus for taking samples from a loop carrying liquid sodium has been described in "Journal of Nuclear Energy", vol. 24 (1970), pages 503 to 508. On pages 607 and 608 of the same journal, further improvements of this apparatus have been proposed, which are to make it suitable for so-called in-line operation, explained below. However, certain shortcomings are inherent in this and other known apparatus of similar kind.
Besides the fact that these prior art embodiments are in general poorly suited for molten metal and that their design is not advantageous for obtaining the vacuum required for the distillation, they have the shortcomings listed as follows: large inside surfaces, at which radioactive residue can form; poor flushing-out of the crucibles, which may make the samples taken unrepresentative, and inaccurate measurement of the temperature of the liquid metal because of the unfavorable arrangement of the thermocouples used for this purpose.
An accurate temperature measurement is important, however, for an exact evaluation of the results of the analysis. It is also doubtful that the desired filling level of the crucibles can be kept accurately with apparatus of the prior art type. In addition, operation is rather awkward, necessitating detaching interfastened flanges connecting the sampling device with the pipe installation, and transporting the entire apparatus to the laboratory. From the German Offenlegungsschrift No. 1,955,988, an improved apparatus of the same type is known which, however, still does not meet all the requirements set forth above. There, the further processing of the samples after they are taken is discussed also.
An object of the present invention is an improved device for taking liquid-metal samples, particularly of molten sodium, where the latter may also be radioactive, and which due to its design adapts the device to the properties of such metal and provides representative samples of the same in a simple and safe manner.